1. Field of the Invention
The present invention relates to a mobile host, a paging agent, a packet communication system, and a movement detection method.
2. Related Background Art
Mobile IP is known as a protocol for controlling transmission and reception of packet data at a Mobile Host (MH) in a communication network (see, for example, [C. Perkins, “IP Mobility Support for IPv4”, Request For Comments 3344, IETF, August 2002] and [RFC3775 “Mobility Support in IPv6”, Network Working Group, June 2004]). According to the Mobile IP protocol, packet reachability from and to a node of the communication counterpart is assumed to be maintained even if MH changes the connecting link along with its movement. In addition, IPP (IP Paging Protocol) is proposed as an expansion of such a Mobile IP protocol.
With the Mobile IP protocol, an MH transmits a Binding Update (BU) to the Home Agent (HA) when changing its connecting link. The HA, managing packet transmission destinations of the MH based on the BU, transfers the communication packets, which were addressed to the MH, to the packet transmission destination thereof.
Additionally, with the IPP protocol, a method is employed which manages the MH for each paging area when the MH is not in communication in order to reduce the amount of communication traffic generated by the BU. The term “paging area” refers to a region in which a BU is not transmitted even if the mobile host moves between networks included in the paging area when the mobile host is not in communication. On the other hand, a method which expands the IPP protocol for mobile communication is proposed (see “Proposal of IP paging in an IP based mobile communication system” by Masahiro Inoue, Ichiro Okajima, Narumi Umeda, Institute of Electronics, Information and Communication Engineers, Communication Society Conference, September, 2003)
When performing movement detection in the network layer of the MH, the above-mentioned Mobile IP protocol and the IP protocol as its expansion use the router discovery protocol, which is one of internet protocol techniques (see JPA 2003-274436 bulletin; “ICMP Router Discovery Messages” by S. Deering, Request For Comments 1256, IETF, September 1991; and “Neighbor Discovery for IP version 6 (IPv6)” by T. Narten, et al., Request For Comments 2461, IETF, December 1998). In other words, the MH receives Router Advertisement information from an access router (AR) existing on the connecting link, and performs movement detection in the network layer based on whether or not the subnet prefix of the IP address of the AR included in the router advertisement information has been changed. Furthermore, when a movement is detected with the IPP protocol, it is also determined whether or not the movement is a crossover between paging areas.